The loading and unloading of road trailer lorries transporting containers is an important part of the operations in almost all container freight terminals. As an operation, the unloading of trailer lorries hardly differs at all from a situation in which the container is picked up in a container depot area, because in both cases the empty container spreader is lowered on to the top of the container, whereupon the container is locked to the spreader with the aid of locking pins.
In automatic container crane systems the container can be lifted automatically from the lorry, for example, with the aid of measuring systems based on laser scanners. However, in most terminals the unloading of containers is a manual operation due to safety provisions.
The loading of trailer lorries is a much more challenging task than unloading. In the trailer of road lorries transporting containers there are usually locking pins making sure that the container will remain in its position during the transportation. Lowering the container with sufficient accuracy, so that the pin holes of the lowered container will come together with the locking pins with sufficient accuracy, is an operation demanding precision. The crane operator's range of visibility is restricted by the container hanging from the container spreader and preventing the operator from seeing the locking pins in the lorry in the late stage of lowering.
Various systems are used to make handling of trailers easier. For example, there are systems where with the aid of a measuring system based on a laser scanner the lorry driver is helped to stop in relation to the crane, so that there is no need to run the primary motions of the crane. Primary motions are those moving the entire portal or lift bogie.
Of prior art solutions representing the laser scanner technology the CN201161875Y printed patent specification is taken as an example, which presents a system for determination of the positions in relation to the crane of the container crane's container spreader and of the trailer lorry to be loaded or unloaded and especially of the locking pins on its platform (or of the container's locking holes). From the information produced by the laser scanners used in the system the type of the lorry to be loaded and/or the type of the container to be lifted off the lorry is also concluded.
A second example of solutions using laser scanner technology is presented in the CN1884034A printed patent specification, which concerns a system for determination of the positions in relation to the crane of a trailer lorry to be loaded or unloaded by a container crane and of containers located on its platform. From the information produced by the laser scanners used in the system the type of the lorry to be loaded and/or the type of the container to be lifted off the lorry is also concluded.
As a third example of solutions representing this technology the JP2005239343A printed patent specification is presented, which concerns a system for determination of the positions of trailer lorries to be loaded or unloaded in relation to the crane handling the containers. The system uses laser scanners located in the crane body.
The container can be lifted automatically from the trailer lorry, for example, with the aid of measuring systems based on laser scanners.
There are also systems based on cameras, which with the aid of computer vision aim at identifying the place of the container determined by locking pins in the trailer. One such solution is presented in the DE3606363A1 printed patent specification, which concerns a system for determination of the position of a trailer lorry to be loaded or unloaded in relation to a crane handling the containers. The system uses cameras located in the crane body at the level of the trailer lorry's platform. The problem with camera-based computer vision systems is their modest reliability due to environmental conditions. Changing lighting, in particular, will cause wrong interpretations. Reliability is very important when controlling the crane's container spreader on the basis of information from the measuring system. Material damages can be caused by false measuring information.
As one more example of the state of the art reference is made to the EP1337454A1 printed patent specification, which presents a system for determination of the position of a trailer lorry to be loaded or unloaded in relation to a crane handling the containers. The system uses sensors located in the crane body at the level of the trailer lorry's platform.